U.S. patent number 4,342,413 [Application Number 06/231,656] was granted by the patent office on 1982-08-03 for turning bar for moving web.
This patent grant is currently assigned to Crown Zellerbach Corporation. Invention is credited to Imants Reba.
United States Patent |
4,342,413 |
Reba |
August 3, 1982 |
Turning bar for moving web
Abstract
Apparatus for providing an air cushion to support web material
during turning thereof and including means defining two plenums
providing a flow path for pressurized gas prior to the gas exiting
from a slit adjacent a generally curved fluid flow attachment
surface. The dual plenum arrangement results in an even air
distribution at the location of the slit thus contributing to web
stability and control as the web floats on a cushion of air
comprised of the pressurized air and ambient air along the
generally curved fluid flow attachment surface due to the Coanda
effect.
Inventors: |
Reba; Imants (Vancouver,
MA) |
Assignee: |
Crown Zellerbach Corporation
(San Francisco, CA)
|
Family
ID: |
22870147 |
Appl.
No.: |
06/231,656 |
Filed: |
February 5, 1981 |
Current U.S.
Class: |
242/615.12;
226/7 |
Current CPC
Class: |
B65H
23/24 (20130101); B65H 2406/111 (20130101) |
Current International
Class: |
B65H
23/24 (20060101); B65H 23/04 (20060101); B65H
017/28 (); B65H 017/32 () |
Field of
Search: |
;226/7,95,97,197
;34/151-156 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Christian; Leonard D.
Attorney, Agent or Firm: Lampe; Thomas R.
Claims
I claim:
1. Apparatus for supporting web material as said web material is
transported and redirected from a predetermined first direction of
movement to a predetermined second direction of movement, said
apparatus comprising:
elongated first plenum defining means having an inlet for the
admission of pressurized gas into said first plenum and an outlet
positioned along the length of said elongated first plenum defining
means for allowing egress of said pressurized gas from said first
plenum;
an elongated housing surrounding and spaced from said elongated
first plenum defining means to define a second plenum therewith in
fluid-flow communication with said first plenum through said
outlet, said elongated housing at least partially defining a slit
providing fluid-flow communication between said second plenum and
the ambient atmosphere; and
means defining a generally curved fluid flow attachment surface
positioned immediately adjacent said slit whereby pressurized gas
exiting from said slit will attach itself to said generally curved
fluid flow attachment surface due to the Coanda effect and provide
along with ambient air entrained by said exiting gas a gaseous
support cushion for said web during transport and redirection
thereof.
2. The apparatus of claim 1 additionally comprising walls
positioned along the edges of said generally curved fluid flow
attachment surface defining means and extending from said slit
whereby lateral loss from said gaseous support cushion is
diminished.
3. The apparatus of claim 1 wherein said generally curved fluid
flow attachment surface defining means at least partially comprises
a curved plate affixed to said elongated housing.
4. The apparatus of claim 1 wherein said curved fluid flow
attachment surface defining means at least partially comprises said
elongated housing.
5. The apparatus of claim 1 wherein said elongated first plenum
defining means comprises a conduit having a generally circular
cross-section and wherein said outlet comprises a plurality of
spaced apertures formed in said conduit along the length
thereof.
6. The apparatus of claim 1 wherein said slit extends
longitudinally along said elongated housing.
7. The apparatus of claim 6 wherein said slit is defined by two
parallel planar slit defining surfaces, at least one of said
surfaces formed on said elongated housing, said surfaces defining
an acute angle with said first direction of web movement.
8. The apparatus of claim 6 additionally comprising means for
variably adjusting the width of said slit along the length
thereof.
9. The apparatus of claim 1 further comprising end caps extending
from said elongated first plenum defining means over said second
plenum and said elongated housing.
10. The apparatus of claim 1 wherein said elongated first plenum
defining means and said elongated housing each comprises conduits,
said conduits being disposed substantially concentrically with
respect to each other.
11. The apparatus of claim 1 wherein said slit and said outlet are
disposed substantially in opposition to each other.
12. The apparatus of claim 11 wherein said second plenum defines a
generally cylindrically-shaped fluid flow path between said slit
and said outlet.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a bar for supporting a movable web as the
web is transported and redirected from a first direction of
movement to a second direction of movement, and in particular, to a
turning bar which generates an air cushion to support, stabilize
and remove wrinkles from the web as it makes the turn.
2. Description of the Prior Art
A variety of systems and devices are known in the prior art for
developing an air cushion to support a moving web as the web
changes direction. The purpose of such air cushion is to support
the web free of engagement with a solid member during web transport
to prevent damage and wear to the web.
Examples of such prior art devices are disclosed in Johnson U.S.
Pat. No. 3,567,093, issued Mar. 2, 1971, Johnson U.S. Pat. No.
3,498,515, issued Mar. 3, 1970, Hamlin et al. U.S. Pat. No.
3,679,116, issued July 25, 1972, Sander U.S. Pat. No. 4,043,495,
issued Aug. 23, 1977, Reba U.S. Pat. No. 4,136,808, issued Jan. 30,
1979, and Daane U.S. Pat. No. 4,197,972, issued Apr. 15, 1980.
Many of the prior art turning bar devices employ a plurality of
apertures or slits in pressurized turning bar housings through
which pressurized air passes and provides a direct support for the
web during transport. It will be appreciated that devices of this
nature use inordinately large amounts of pressurized air to
accomplish the purpose of web support and are consequently
inefficient and expensive to operate. In addition, such devices,
due to uneven air distribution found at the turning bar surface,
can cause wrinkling and other deformations to occur in the web.
Prior art devices are also often characterized by even greater
inefficiencies when operating at high speeds.
In the above-noted U.S. Pat. No. 4,197,972, issued to Daane, a
turning bar device is illustrated which utilizes the Coanda effect
to provide an air cushion for a web. When utilizing the Coanda
effect ambient air is entrained to provide a portion of the web
cushion and thus operating efficiencies are attained. The present
invention also relates to a turning bar arrangement employing the
Coanda effect to provide an air cushion. The present invention,
however, employs a specific arrangement for bringing the Coanda
effect into play, an arrangement that is specifically adapted to
ensure even air distribution to the Coanda nozzle forming a
component of the turning bar. Even air distribution is important to
maintain proper web stability and control as the web makes the turn
about the bar. In the present invention web control can be readily
accomplished without the necessity of employing air nozzles
disposed along the edges of web travel as is the case in Daane to
eliminate side drift or lateral tracking instability of the web as
well as to ensure predetermined desired spacing of the web with
respect to the turning bar.
Another feature of the present invention resides in the employment
in the turning bar of means to crown the web as it makes the turn,
thus removing wrinkles therefrom and contributing to web
stabilization. The invention is particularly useful with wet coated
webs wherein contact could disrupt or cause defects in the
coating.
BRIEF SUMMARY OF THE INVENTION
Apparatus constructed according to the teachings of the present
invention includes an elongated first plenum defining means having
inlet and outlet openings therein, an elongated housing surrounding
and spaced from the elongated first plenum defining means to define
a second plenum therewith in fluid flow communication with the
first plenum through the outlet means, and means defining a curved
fluid flow attachment surface positioned immediately adjacent to a
slit formed in the housing in communication with said second
plenum. The dual plenum arrangement of the present invention is so
constructed as to allow even distribution of air to the housing
outlet slit thereby providing a precisely controlled air cushion
for the web being turned about the apparatus. The air cushion is
comprised of the pressurized air passing through the housing
restricted outlet slit and ambient air entrained thereby. The air
cushion attaches itself to the curved fluid flow attachment surface
due to the Coanda effect. Means is preferably provided to vary slit
width along the length thereof to provide more pressurized air at
the center of the web than at the edges thereof, thus serving to
crown the web.
DESCRIPTION OF DRAWINGS
FIG. 1 is a plan view of the preferred form of apparatus
constructed in accordance with the teachings of the present
invention;
FIG. 2 is a cross sectional view taken along line 2--2 in FIG.
1;
FIG. 3 is an enlarged detail view of the means defining a
restricted opening in the apparatus housing and related structure
as taken along line 3--3 in FIG. 1; and
FIG. 4 is a view similar to that of FIG. 2 but illustrating an
alternative embodiment.
DETAILED DESCRIPTION
In FIGS. 1-3 apparatus constructed in accordance with the teachings
of the present invention includes first plenum defining means 10 in
the form of an elongated conduit formed of any suitable material
such as aluminum. At one or both outer ends thereof means 10 is
supported by a suitable housing (not shown). At at least one end
thereof, and preferably at both ends thereof, the interior or
plenum defined by means 10 is selectively placed in communication
with any suitable source of pressurized air such as an air
compressor (not shown). Pressurized air entering the first plenum
defining means 10 will be caused to exit therefrom through a
plurality of air distribution slots or apertures 12 formed along
the length of means 10.
Surrounding elongated first plenum defining means 10 and spaced
therefrom is a housing 14 which is also preferably in the general
shape of a conduit formed of aluminum or other suitable material.
Housing 14 and first plenum defining means 10 are commonly
connected by end caps 15 and 17 and cooperate to form a generally
cylinderically shaped second plenum 16 therebetween. Apertures 12
provide fluid flow communication between the first plenum and
second plenum 16.
As may be seen most clearly with reference to FIG. 2, housing 14
forms a gap 20 near the upper end thereof substantially
diametrically opposite to the locations of apertures 12 in the
elongated first plenum defining means 10. Gap 20 extends along the
full length of housing 14. A plate 22 is secured to housing 14 as
by means of screws 23 or any other suitable expedient to generally
cover the gap along its length. The free end of plate 22 projects
over a first planar surface 26 formed on housing 14 as shown in
detail in FIG. 3. The bottom of plate 22 forms a second planar
surface 28 which is parallel to first planar surface 26 and defines
an elongated slit therewith. Second planar surface 28 converges
with a third planar surface 29 formed on housing 14 at a
predetermined angle which may be in the order of 30 degrees for
example.
It will be appreciated that pressurized air in second plenum 16
will exit from the slit defined by planar surface 26 and 28 as a
thin high speed gaseous flow at an acute angle with respect to the
direction of a web W as the web passes over the slit in a
predetermined first direction of movement (generally horizontal
direction in the drawing). After exiting from the slit the
pressurized gas will attach itself to a generally curved fluid flow
attachment surface defined in part by fourth and fifth planar
surfaces 30 and 32 formed on housing 14. In a representative
construction of the turning bar, surface 30 diverged from planar
surfaces 26 and 28 an angle of 17 degrees and surface 32 by an
angle of 40 degrees, although this may be varied as necessary. As
shown in FIG. 2 planar surface 32 merges into and is contiguous
with the outer curved surface 38 of curved deflection member 40
mounted in a recess 42 formed in housing 14. It will be appreciated
that the pressurized gas passing through the slit and ambient air
entrained thereby will attach to the generally curved surface as
defined by surfaces 30, 32 and 38. The air cushion will direct the
web from a predetermined first direction of movement shown at the
upper left end of FIG. 2 to a second predetermined direction
assumed by the web W at the location shown at the right side of
FIG. 2 where the web exits from curved deflection member 40.
It should be noted that web W is brought into close proximity with
the turning bar at a location downstream from the slit whereat the
air cushion is moving substantially the same direction as the web.
If web W were to approach the slit too closely it would be
subjected to undesirable suction forces that would tend to pull the
web downwardly. If desired, suitable adjustment mechanism (not
shown) may be associated with the turning bar to enable an operator
to "fine tune" positioning of the bar slit relative to the web to
optimize results.
Lateral air loss from the cushion supporting web W is prevented by
employing two sidewalls 46 and 48 along the edges of the generally
curved fluid flow attachment surface. Additional control over the
characteristics of the air cushion may be provided by employing a
suitable means of varying the width of the slit along its length to
establish a desired air flow profile. It has, for example, been
found that by making the slit wider in the center than at the
edges, more air cushioning in the middle of the web is obtained
which creates cross machine spreading and improved guiding of the
web. In essence, this provides for a crowning effect in the web
whereby wrinkles will be removed. The turning bar may thus be used
to accomplish the objectives of a far more expensive Mount Hope
roll without contact with the web. Slit thickness variations may be
accomplished through the use of any suitable expedient such as the
employment of shims 50 or a screw adjustment mechanism of the type
shown in my U.S. Pat. No. 4,186,860, issued Feb. 5, 1980.
As indicated above it is highly important that pressurized air be
evenly distributed in the system at the point where it is
introduced into the slit. The dual plenum arrangement of the
present system as described above serves to accomplish this. It
will be appreciated that air exiting from apertures 12 divides into
two segments as shown by the arrows in FIG. 2 and flows within the
second plenum 16 until the vicinity of the gap 20 is reached. Such
flow path tends to dampen out and even any flow anomalies that may
have been created along the length of the system prior to passage
of the pressurized air through the slit.
FIG. 4 shows an alternative embodiment of the present invention.
This embodiment differs from that shown in FIGS. 1-3 only by virtue
of the fact that it employs a cambered curved deflection member 54.
It has been found that such cambered configuration can be used to
further improve web turning efficiency, i.e. the extent of arc over
which the web floats without contact, by virtue of the fact that
air flow will be modified at the point of camber to hold the web W
against the deflection member over a longer length. This occurs
because the Coanda effect causes the air cushion to bend inwardly
at the location of camber.
* * * * *